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CMIT/MIT (Methylchloroisothiazolinone/Methylisothiazolinone 3:1)

  • Preservatives
  • CAS 55965-84-9
  • IUPAC: Mixture of 5-chloro-2-methyl-2H-isothiazol-3-one and 2-methyl-2H-isothiazol-3-one (3:1)

Acute Tox. 3 (H301), Skin Corr. 1C (H314), Skin Sens. 1A (H317), Acute Tox. 2 (H310/H330) at ingredient level — among the most hazardous preservatives by GHS classification. The H317 skin sensitization is the primary product-level concern at typical use concentrations (<0.0015%) — even those trace levels can elicit allergic reactions in sensitized individuals.

CMIT/MIT (Kathon CG) is a broad-spectrum biocide preservative widely used in water-based cleaning and personal care products. It is effective at extremely low concentrations (typically <0.0015% / 15 ppm), which is why it remains in use despite its severe ingredient-level GHS classifications. The H317 skin sensitization potency is high; CMIT/MIT is one of the most common causes of allergic contact dermatitis identified in patch-testing clinics. The EU has banned it from leave-on cosmetic products and tightly restricts it in rinse-off products; US regulation is less strict. Per the leather-cleaner health rubric, CMIT/MIT presence in SDS Section 3 triggers the H317 deduction (−1.0) regardless of finished-product concentration.

Health & environment profile

VOC
no
Prop 65 listed
no
Asthmagen
no
EPA Safer Choice
no
Aquatic toxicity
yes
Biodegradable
no
Bioaccumulative
no
Persistent
yes
Ozone depleting
no
Microplastic
no
PFAS
no
Env. score
2/5
Purpose: Broad-spectrum biocide preservative for water-based formulations; effective at very low concentrations (typically <0.0015%)

2 products contain this

Health summaries are editorial — we synthesize from SDSs, peer-reviewed sources, and regulatory listings. Not medical advice.